In certain types of jet aircraft, turbine engines are mounted to structures suspended from the aircraft wings. Generally, so-called rigid mounting bracket assemblies which do not isolate vibration have been used because space was not available for either a flexible isolator design or for the engine motion which it allowed. A feasible vibration isolating engine mount is frequently required to support lateral and vertical loads from engines weighing 10,000 pounds or more, with take-off thrust of the order of 60,000 pounds. Spring rates in the lateral and vertical directions must meet values required by dynamic vibration analyses within .+-.15%. Engine motion must not exceed limits such as .+-.0.20 inches, even under loads as high as 35,000 pounds, without failure. When only one front and one rear mount are used in conjunction with the thrust links, the rear mount may be required to provide a roll spring rate of 10,000,000 inch pounds per radian, yet still have lateral and vertical spring rates of only 70,000 pounds per inch. Typically, all of this must fit within a space envelope 11" .times. 16" .times. 5" high. In addition to meeting these requirements, the mounting brackets must accommodate severe operating conditions, including high temperatures and vibrations.
Various structures have been proposed for mounting turbine engines to aircraft. Examples of such structures may be found in the following U.S. Pat. Nos.: 3,288,404; 3,368,270; 3,727,862; 3,831,888; 4,013,246; 4,022,018; 4,437,627; 4,603,821; and 4,603,822.
U.S. Pat. No. 3,288,404, issued to Schmidt and owned by the assignee of the present application, discloses a turbine engine mounting system which is used on a helicopter. The mounting system includes a torque tube supported in an elastomeric bearing and having arms extending therefrom for connection to an engine bracket.
U.S. Pat. No. 4,805,851, issued to Herbst, and owned by the assignee of the present application, discloses a turbine engine mounting system which is particularly suited for mounting turbine engines to struts suspended from the wings of jet aircraft. In this patented system, a pair of arms are connected by a torque tube which is embraced by an elastomeric bearing of a particular configuration that permits the arms to pivot about the axis of the torque tube but restricts independent pivoting to a minimum. In this way, the torque tube provides roll stiffness, i.e. reactivity to torquing of the engine about its longitudinal axis, and reactivity to torque due to lateral gusts and side loads, while supporting lateral and vertical engine loads with relatively lower spring rates. A particularly desirable feature of the Herbst mount is its ability to limit the transmission of engine vibration noise to the cabin of the aircraft.
While the aforementioned Herbst engine mount functions satisfactorily for its intended purpose, there are aircraft engine mounting applications which require an even larger roll stiffness, greater vibration attenuation, and longer life as well as vertical and lateral load support for engines of higher thrust than those with which the Herbst mount currently finds utility. The present invention provides an engine mounting assembly which meets these requirements.